Influence of Different Heat Treatments on Torsional and Cyclic Fatigue Resistance of Nickel–Titanium Rotary Files: A Comparative Study

Abstract

Protaper Universal (PTU), Protaper Gold (PTG) (Maillefer, Ballaigues, CH), EdgeTaper (ET), and EdgeTaper Platinum (ETP) (Albuquerque, NM, USA) were tested for both torsional and flexural resistance. The aim of the present study was to evaluate the influence of proprietary heat treatment on the metallurgical properties of the aforementioned instruments. Four groups of 30 different instruments (size 20.07) were tested, then divided into two subgroups of 15 instruments—one for the cyclic fatigue test in a curved canal (90°—2 mm radius) at 300 rpm and 2.5 Ncm. The time to fracture (TtF) and fragment length (FL) were recorded. The other subgroup was subjected to the torsional test (300 rpm, 5.5 Ncm). The torque to fracture and TtF were recorded. All the instruments underwent a SEM analysis. The heat-treated instruments showed a significantly higher fatigue resistance than the non-heat-treated instruments (p < 0.05). No significant differences were found in the torsional resistance between the ET and PTU, and the ETP and PTG. However, when comparing all the groups, the heat-treated instruments showed less torsional resistance. The improvement from heat treatment was mainly found in the cyclic fatigue resistance.

An Update on Nickel-Titanium Rotary Instruments in Endodontics: Mechanical Characteristics, Testing and Future Perspective—An Overview

“…Finally, the second group consists of all those structural factors that characterize an endodontic instrument, such as the cross-sectional design, the type of the alloy and its crystallography phase, the manufacturing processes, the pitch, the helix and the rake angle, the length of the instrument and the taper [ 49 , 55 , 62 , 63 , 64 ]. As many studies have shown, the design of the cross-section is one of the most important parameters that can significantly determine the torsional stiffness of a NiTi endodontic instrument, since it thoroughly influences its mechanical properties [ 62 , 65 , 66 ].…”

3D Finite Element Analysis of Rotary Instruments in Root Canal Dentine with Different Elastic Moduli

“…Regarding the different instruments Hyflex CM and One Curve showed the best mechanical rotating behaviors. Recent in vitro investigations [39] confirmed, from a mechanical viewpoint, the influence of different heat treatments on the torsional and cyclic fatigue resistance of rotary instruments.…”

Nickel–Titanium Rotary Instruments: An In Vitro Comparison (Torsional Resistance of Two Heat-treated Reciprocating Files)

“…4,6 For this reason, in recent literature many studies focused their attention on NiTi torsional behavior. 7,8 Recent studies investigated the role of two prevailing factors affecting torsional resistance, that is, heat treatments and the metal mass of the instrument. [7][8][9] According to the most recent literature, static torsional resistance tests have been evaluated as described by International Organization for Standardization (ISO) 3630-1.…”

“…7,8 Recent studies investigated the role of two prevailing factors affecting torsional resistance, that is, heat treatments and the metal mass of the instrument. [7][8][9] According to the most recent literature, static torsional resistance tests have been evaluated as described by International Organization for Standardization (ISO) 3630-1. According to this, to evaluate torsional resistance, a stainless steel (SS) instrument is rotated at 2 rpm with its tip blocked at 3 mm until fracture and the torque generated is calculated by a torque meter.…”